The invention relates to an adaptive mirror based on a ceramic substrate having a corresponding reflector and piezoelectric actuators, a cooling device being integrated in the substrate. The invention likewise relates to a method for the production of such mirrors. The mirrors according to the invention are used for the modulation or deformation of a laser wavefront of high power.
One solution to the modulation of a laser wavefront with high powers with the help of an adaptive mirror was developed by A. V. Ikramov. A. V. Ikramov et al., “Bimorph adaptive mirror”, Soy. J. Quantum Electron. 22(2), February 1992 describes a cooled adaptive mirror which consists of a substrate plate (copper) and a reflective disc on the substrate upper side and two piezoelectric discs on the underside.
The substrate plate has cooling channels with cooling liquid and thus functions as a cooling plate. The lower of the two piezoelectric discs is subdivided into an outer and an inner ring, whilst the upper of the two discs is subdivided into 17 parts and was contacted. Due to the cooling and the lower piezoelectric disc, the initial position of the mirror surface can be stabilised and the thermal deflection which is caused by the high power input of the reflected radiation are compensated for. The upper piezoelectric disc compensates for the deformations of the wavefront of a higher order.
The cooling has consisted to date merely of metallic substrates, such as copper or tungsten. Thus WO 02/35274 A1 describes a mirror, in particular for high power lasers, having an adjustment device for correcting the curvature of the mirror and having a cooling device which was produced by cutting methods and is intended to be situated close to the heat introduction. The supply and discharge line of the cooling medium is effected via the webs of the mirror suspension. The actuators act either at points or over the surface, but in any case perpendicular to the mirror surface. The industrial right US 000004674848 A was also conceived for use as laser mirror and has piezoelectric stacked actuators which act perpendicular to the mirror surface.
EP 07 93 120 A1 describes an adaptive bimorph mirror for use in laser systems and in astronomy telescopes. The mirror substrate and the mirror frame are manufactured from one piece, the height of the suspension of the mirror being thinned close to the fixing and thus having a predetermined breaking point which can also in addition be structured. The mirror frame can function as heat sink and thus cool the mirror membrane.
These systems known from the state of the art involve the disadvantage that high manufacturing complexity is associated with the use of metallic substrates. Thus, metals, in particular copper, in fact have good thermal conductivity but they also have a high thermal inherent expansion. In addition, it is disadvantageous that the effect of the piezoelectric actuators can be weakened by the great substrate height.